/Engine/Source/Runtime/GeometryCore/Public/DynamicMesh/DynamicVertexSkinWeightsAttribute.h
Set the value at an Attribute to be a barycentric interpolation of three other Attributes. If one of the barycentric coordinates is nearly one (within UE_SMALL_NUMBER tolerance) then simply copy over the value of the corresponding Attribute.
void SetBoneWeightsFromBary ( int SetAttribute, int AttributeA, int AttributeB, int AttributeC, const FVector3d & BaryCoords )